Description:
We have shown that neural ectoderm cells, brain and spinal cord precursors, remain plastic and responsive toward muscle inducing signals during gastrulation. However, the duration and parameters of this plasticity after gastrulation remain unclear. We hypothesize that like other developmental processes, neural fate specification occurs in an anterior to posterior fashion and that time and space act to differentially regulate cell plasticity. Fluorescently labeled cells from the anterior neural ectoderm grafted to a prospective muscle region lose the ability to form muscle fibers by the end of gastrulation (stage 12.5); whereas posterior neural ectoderm cells lose the ability to form muscle fibers near the end of neurulation (stage 18). By varying the developmental stage of the donor cells we are able to show that the anterior neural ectoderm cells lose their plasticity prior to posterior neural ectoderm cells. Varying the temporal and spatial placement of the grafted neural ectoderm cells tests the parameters of plasticity during the highly dynamic process of development. The ability of neural ectoderm cells (both anterior and posterior) to differentiate into muscle drastically declines when cells are grafted to a younger host embryo or to a more ventral area within the muscle fated region. This indicates that neural ectoderm cells and perhaps other plastic cell types need to be immediately exposed to inductive signals in order to efficiently change cell fate. These results offer new insights into the ability of embryonic cells to regulate plasticity during development.